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Increase and Decrease Numbers by a Given Percentage

In this worksheet, students will practise increasing and decreasing numbers by the given percentages. They can use a calculator to help.

'Increase and Decrease Numbers by a Given Percentage' worksheet

Key stage:  KS 3

Year:  Year 8 Maths worksheets

Curriculum topic:   Number

Curriculum subtopic:   Define, Interpret and Compare Percentages

Difficulty level:  

Worksheet Overview

In this activity, we will learn how to increase and decrease numbers by a given percentage using a calculator.


Methods and Examples

A whole number or quantity is 100%.

Increasing a number by 10% gives 100% + 10% = 110% of the number or 1.1 × the number.


diagram to show a percentage increase


So 25 cm increased by 10% is 1.1 × 25 = 27.5 cm.


Decreasing a number by 15% gives 100% - 15% = 85% of the number or 0.85 × the number.


 diagram to show percentage decrease


So 25 cm decreased by 15% is 0.85 × 25 = 21.25 cm.


Let's try one more example of each, shall we?


What is 73% increased by 25%? 25% extra means 100% plus 25% which makes 125%. So we need to multiply by 1.25, we say that our multiplier is 1.25.

73 x 1.25 = 91.25


What if 73% decreased by 16%?

100 - 16 = 84, so our multiplier becomes 0.84

73 x 0.84 = 61.32


Does this make sense? Let's have a go at some questions then and if you need to check back to these instructions, just click on the red button at any point.


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